1. Field of the Invention
The present invention relates to a fuel injection control system for a compressed natural gas-fueled automotive vehicle using compressed natural gas (CNG) as a fuel.
2. Description of the Related Art
A compressed natural gas-fueled vehicle uses compressed natural gas instead of the gasoline as a fuel. The compressed natural gas is mixed with air in an intake manifold and supplied to the engine. In the compressed natural gas-fueled vehicle, high-pressure natural gas is stored in a tank. For this reason, a sensor for detecting the gas pressure is included for fail-safe control such as closing a gas shutoff valve when the gas leaks. This fail-safe control operation is not performed in the case where the gas is consumed to such an extent that the residual gas amount has been reduced to a very small level.
In the case where the residual amount of gas has reached to a very small level, however, a misfire may occur due to the fuel shortage in the engine. If a high load operation (high-speed run, for example) of the vehicle is continued under this condition, the uncombusted gas which may be discharged from the engine into a catalyst unit is burnt by a catalyst already very high in temperature. Thus, the catalyst is heated to an abnormal temperature and thus may give rise to a breakdown of the catalyst unit or another problem may result.